1. Field of the Invention
This invention relates to improvements in a display system for optically projecting a display light of information to be observed by a person from a liquid crystal display as a display device, and more particularly to the display system such as a head-up display system which is configured, for example, such that an operator and the like can observe an image of driving information projected as the display light on a windshield glass or on a combiner provided on the windshield glass while looking a frontal view through the windshield glass in such a manner that the driving information is superimposed on the frontal view, in a vehicle or a ship, or the like display system for architecture.
2. Description of the Prior Art
A variety of head-up display systems of an automotive vehicle have been hitherto proposed and put into practical use. A typical head-up display system is constituted by directly applying a film functioning as a half mirror on a windshield glass, or by interposing the half mirror between two glass plates. However, with this head-up display system, reflection of light of an image is unavoidably made on the front-side or rear-side surface of the glass plate thereby forming a double image which is difficult to be observed by a driver. In view of this, another types of the head-up display system have been proposed, in which light of the image is reflected from the surface of the glass plate without using the half mirror in order to avoid formation of the double image. One of these is configured by applying a so-called xcex/2 film (for changing a direction of polarization of light) on a transparent plate such as a glass plate, as disclosed in Japanese Patent Provisional Publication No. 2-141720 Another one is configured by bonding a transparent film having birefringence on a transparent plate, as disclosed in Japanese Patent Provisional Publication No. 2-294615. A further one is configured by bonding a optical rotation layer formed of a crystalline high polymer on a transparent plate, as disclosed in Japanese Patent Provisional Publication No. 6-40271. Additionally, some of the inventors of this application have proposed a display system including a combination of an optical rotation film, a light-transmittable reflection film and an antireflection film, as disclosed in a United States Patent Application No. 08/621379 entitled xe2x80x9cGlass Arrangementxe2x80x9d.
The above display systems usually employs a fluorescent display tube or a liquid crystal display as the displaying device for generating the display light of information to be incident on the glass plate.
However, widely used liquid crystal displays except for some small-sized televisions using a liquid crystal display are so set that the axis (plane) of polarization is generally oblique relative to a vertical axis and a horizontal axis of the image plane of the liquid crystal display, i.e., generally along a diagonal line of the image plane in order to keep a bilateral symmetry of angle of visibility. Accordingly, it is impossible to prevent formation of the double image by using the conventional optical rotation film capable of rotating the plane of polarization about 90xc2x0. In order to prevent formation of the double image, it is required to use a small-sized liquid crystal display having an axis (plane) of polarization vertical or horizontal in the image plane of the liquid crystal display, or to use a specially prepared liquid crystal display whose axis of polarization is adjusted only corresponding to the display system.
It is an object of the present invention to provide an improved display system which can effectively overcome drawbacks encountered in conventional display systems such as a head-up display system.
Another object of the present invention is to provide an improved display system which is simple in construction and can effectively prevent formation of a double image to be recognized by an operator, even by using a usual liquid crystal display whose axis (plane) of polarization is inclined about 45xc2x0 relative to a vertical axis on the image plane of the liquid crystal display.
An aspect of the present invention resides in a display system, comprising a transparent plate. A liquid crystal display is provided for generating a display light of information. The display light has a plane of polarization inclined by an angle of about 45xc2x0 relative to a vertical axis of an image plane of the liquid crystal display. A first optical rotation layer is disposed on a first surface of the transparent plate. The optical rotation layer is adapted to receive the display light from the liquid crystal display and to optically rotate the plane of polarization of the display light by an angle of about 90xc2x0. A second optical rotation layer is disposed between the image plane of the liquid crystal display and a second surface of the transparent plate. The optical rotation layer is adapted to optically rotate the plane of polarization of the display light from the liquid crystal display by an angle of about 45xc2x0 and to allow S-polarized light to emanate toward the transparent plate at Brewster""s angle. The S-polarized light is reflected on a side of the second surface of the transparent plate to be directed toward an eye of an operator.
Another aspect of the present invention resides in a display system comprising a transparent plate. A liquid crystal display is provided for generating a display light of information. The display light has a plane of polarization inclined by an angle of about 45xc2x0 relative to a vertical axis of an image plane of the liquid crystal display. A first optical rotation layer is disposed to a second surface of the transparent plate. The optical rotation layer is adapted to optically rotate the plane of polarization of the display light incident thereon by an angle of about 90xc2x0. The display light from the first optical rotation layer is reflected on the second surface of the transparent plate and directed toward an eye of an operator. Additionally, a second optical rotation layer is disposed between the image plane of the liquid crystal display and a second surface of the transparent plate. The second optical rotation layer is adapted to optically rotate the plane of polarization of the display light from liquid crystal display by an angle of about 45xc2x0 and to allow P-polarized light to outgo toward the first optical rotation layer at Brewster""s angle.
A further aspect of the present invention resides in a display system comprising a transparent plate. A liquid crystal display is provided for generating a display light of information. The display light has a plane of polarization inclined by an angle of about 45xc2x0 relative to a vertical axis of an image plane of the liquid crystal display. The display light is incident on a second surface of the transparent plate at Brewster""s angle and reflected on a side of the second surface of transparent plate to be directed to an eye of an operator. An optical rotation layer is disposed to a first surface of the transparent plate. The optical rotation layer is adapted to receive the display light from the liquid crystal display and to optically rotate the plane of polarization of the display light from the liquid crystal display by an angle of about 45xc2x0 and to allow P-polarized light to outgo therefrom.